Microlithography projection system with an accessible diaphragm or aperture stop

ABSTRACT

The invention relates to a microlithography projection lens for wavelengths &lt;=248 nm &lt;=, preferably &lt;=193 mm, in particular EUV lithography for wavelengths ranging from 1-30 nm for imaging an object field in an object plane onto an image field in an image plane, the microlithography projection lens developed in such a manner that provision is made for an accessible diaphragm plane, into which for instance an iris diaphragm can be introduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims benefit to U.S.application Ser. No. 11/851,852, filed Sep. 7, 2007, which is acontinuation of International Application No. PCT/EP2006/002005, filedMar. 4, 2006, which claims benefit to U.S. Provisional Application No.60/659,660, filed Mar. 8, 2005. The contents of these applications arehereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a microlithography projection system, aprojection exposure system and a chip manufacturing method.

2. Description of Related Art

Lithography employing wavelengths ≦248 nm, preferably ≦193 nm, inparticular EUV lithography employing λ=11 nm and/or λ=13 nm, isdiscussed as a possible technique for imaging structures <130 nm, ormore highly preferable <100 nm. The resolution of a lithographic systemis described by the following equation:

${{R\; E\; S} = {k_{1} \cdot \frac{\lambda}{N\; A}}},$where k₁ designates a specific parameter of the lithographic process, λthe wavelength of the incident light and NA the image-side numericalaperture of the system.

The optical components of EUV imaging systems are essentially reflectivesystems employing multilayer coatings. Mo/Be systems are the preferredmultilayer coating systems employed for λ=11 nm and Mo/Si systems forλ=13 nm. Lithography with wavelengths below 11 nm is possible.

In order to achieve the highest resolution possible, it is necessary forthe system to have an image-side aperture that is as large as possible.

It is an advantage for a lithographic system if the optical path withina projection system or projection lens is free of vignetting orobscuration. The disadvantage of systems with a vignetted exit pupil,e.g. so-called Schwarzschild mirror systems, is that structures of aparticular magnitude can only be imaged with reduced contrast. The exitpupil is defined as the image of the aperture stop, imaged by amicrolithography projection system located in the optical path betweenthe aperture stop and the image plane.

For instance, 4-mirror systems for microlithography are known from US2003/0147130, US 2003/0147149, U.S. Pat. No. 6,213,610, U.S. 6,600,552or U.S. 6,302,548. Systems of this kind are provided with a diaphragmarranged in the optical path from an object plane to an image plane infront of the first mirror of the projection system, a so-called ‘frontstop’. A front stop has the disadvantage that it results in either asystem with a large overall construction length or a large chief rayangle at the object. A large construction length prevents theconstruction of a compact and space-saving system and a large chief rayangle at the object generates significant vignette effects when using areflective mask because the thickness of the absorbent structure mountedon the reflective multiple layers is not negligible.

6-mirror systems for microlithography are known from the publicationsU.S. Pat. No. 6,353,470, U.S. 6,255,661, US 2003/0147131 and US2004/0125353.

In U.S. Pat. No. 6,353,470 the diaphragm lies either on a mirror orbetween two mirrors, where the distance to a beam of light extending inthe vicinity of the diaphragm from one used area of a mirror to a usedarea of a subsequent mirror in the optical path is <5% of theconstruction length of the projection system. The construction length orthe structural length of a projection system is defined in thisapplication as the axial distance measured along the optical axis (HA)of the projection system from the object plane to the image plane. For aconventional construction length of 1000 mm to 1500 mm for such asystem, the radial distance between the aperture stop and a passing beamof light amounts to less than 50 mm or 75 mm, respectively. Within thescope of this application, the radial distance of a used area or anaperture stop from a beam of light is defined as the perpendiculardistance with respect to the optical axis from a beam of light which isclosest to the boundary of the used area or the aperture stop as shownin FIG. 4 b. U.S. Pat. No. 6,255,661 discloses the provision of anaperture stop between the second and third mirror. However, in this casethe radial distance to a beam of light extending in the vicinity of theaperture stop from one used area of a mirror to a second used area of asubsequent mirror positioned in the optical path amounts to less than 5%of the construction length of the projection system.

In the case of the 6-mirror system disclosed in US 2003/0147131, theaperture stop lies on the second mirror or between the first and thesecond mirror. With an arrangement between the first and the secondmirror, the radial distance of the aperture stop to the optical pathfrom the object to the first mirror and to the optical path from thesecond to the third mirror is less than 5% of the construction length ofthe projection lens.

U.S. Pat. No. 6,781,671 discloses a 6-mirror system that has a aperturestop arranged between the second and third mirror. The radial distanceof the aperture stop to the optical path from the first to the secondmirror is less than 11% and the radial distance of the aperture stop tothe optical path from the third to the fourth mirror less than 32% ofthe construction length. The chief ray angle at the diaphragm is greaterthan 26°. In the present application the chief ray angle at thediaphragm or aperture stop is defined as the angle at which the chiefray of the central field point passes through the diaphragm plane inwhich the diaphragm or aperture stop is arranged.

U.S. Pat. No. 6,781,671 discloses an 8-mirror system that has a aperturestop arranged between the second and third mirror. The radial distanceof the aperture stop to the optical path that extends from the first tothe second mirror, amounts to less than 12%, and the distance of theaperture stop to the optical path from the third to the fourth mirror isless than 16%. The chief ray angle at the aperture stop is greater than24°.

Further 8-mirror systems for microlithography are known from US2002/0129328 or U.S. Pat. No. 6,556,648. In these systems the aperturestops are always positioned on a mirror.

U.S. Pat. No. 5,686,728 shows an 8-mirror system having an aperture stopbetween the second mirror and the third mirror, but the radial distanceof the aperture stop in this system to the optical path of a beam oflight extending in the vicinity of the aperture stop, is less than 1% ofthe construction length of the projection system.

Systems, as described above, in which the aperture stop lies on or neara mirror, have the disadvantage that an adjustable aperture stop designcan only be technically implemented at a certain minimum distance of thediaphragm in front of a mirror. Consequently, the light passes throughan aperture stop arranged in the optical path in this manner twice: oncedirectly in front of the mirror and once directly after the mirror. Thisresults in vignetting by the diaphragm that becomes apparent forinstance in H-V differences. In order to prevent this vignetting, asingle-pass diaphragm or aperture stop is advantageous from an opticalstandpoint, in particular with high aperture systems.

A single-pass aperture stop for an 8-mirror system is shown in U.S. Pat.No. 5,686,728. The aperture stop in U.S. Pat. No. 5,686,728 is arrangedbetween the second mirror and the third mirror in the front section ofthe system. The disadvantage of this embodiment is, however, the largechief ray angle at the diaphragm, which is approximately 34° for animage-side NA of 0.5. The large chief ray angle at the aperture stop inU.S. Pat. No. 5,686,728 is attributable to the minimal axial distancebetween the second mirror and the third mirror. In order to ensure anobscuration-free optical path in the case of U.S. Pat. No. 5,686,728, itis necessary to physically split the beam of light at the aperture stopfrom the first mirror to the second mirror, from the second mirror tothe third mirror and from the third mirror to the fourth mirror. Inorder to achieve this, the projection system has a large chief ray angleat the aperture stop as this results in a smaller aperture diameter,owing to the fact that the product of the chief ray angle and thediameter of the beam of light is a constant. However, a large chief rayangle at the aperture stop has disadvantages. For instance, a largechief ray angle causes a large telecentric error when the diaphragm isdisplaced along an x, y or z axis. A further disadvantage is that alarge chief ray angle means the diameter of the aperture stop is small.This has technical manufacturing disadvantages as requirements withrespect to the precision of shaping measured in absolute units are verystringent for aperture stops or diaphragms with a small diameter. Incontrast, a small chief ray angle means a large aperture diameter andless stringent requirements with respect to precision of shaping ormould precision.

SUMMARY OF THE INVENTION

The disadvantage of all known systems involving a aperture stop ordiaphragm arranged between two mirrors is that there is insufficientspace for installing e.g. an iris stop as the distance to the beam oflight extending in the proximity of the aperture stop or diaphragm istoo small.

One aspect of the invention is to disclose a microlithography projectionsystem without the above-mentioned disadvantages.

In a further aspect of the invention a microlithography projectionsystem is disclosed that provides an location e.g. an diaphragm planefor the installation of an easily accessible diaphragm e.g. theinstallation of an iris stop.

In this application a diaphragm describes an element with which a lightbundle that passes through a diaphragm plane can be influenced. Such anelement can be e.g. an aperture stop, especially an iris stop or a greyfilter, which modulates light.

Since in this application the diaphragm plane is a plane which issituated in or near a conjugated plane to the exit pupil plane of theprojection system in general by the diaphragm the pupil-image in theexit pupil can be influenced.

In even a further aspect of the invention a projection system isdisclosed that allows a broad tolerance with respect to diaphragmposition and precision of shaping of a diaphragm.

In a further aspect of the invention a microlithography protectionsystem should be provided which allows for the correction of thepupil-image, e.g. the correction of telecentricity and the distortion inthe exit pupil plane.

In a first embodiment of the invention for solving at least one of theabove mentioned aspects a microlithography projection system especiallyfor wavelengths ≦248 nm, preferably ≦193 nm, in particular EUVlithography for wavelengths ranging from 1-30 nm, for imaging an objectfield in an object plane onto an image field in an image plane isprovided, wherein the microlithography projection system comprising atleast three mirrors (S1, S2, S3) with a used area (N1, N2, N3), whereinrays of a light beam that pass through the projection system from theobject plane to the image plane in an optical path impinge upon at leastone of each of the used areas (N1, N2, N3), and wherein a diaphragm (B)is arranged in a diaphragm plane (1000), wherein a first section of theoptical path between a first used area (N1) and a second used area (N2)passes the diaphragm plane and wherein said diaphragm plane (1000) isonly further passed by a second section of the optical path between asecond used area (N2) and a third used area (N3) above or below thefirst section of the optical path. Such an embodiment allows for adiaphragm or aperture stop to be provided in the diaphragm plane whichis easily accessible at least from one side.

In a further embodiment of the invention one of the above mentionedaspects is solved by means of a microlithography projection systemespecially for wavelengths ≦248 nm, preferably ≦193 nm, in particularfor EUV lithography for the preferred wavelengths ranging from 1-30 nm,for projecting an object field in an object plane onto an image field inan image plane, with the microlithography projection system comprisingat least three mirrors, with the rays of a beam of light passing throughthe projection system from the object plane to the image plane toimpinge upon a used or a useful area of each of the said mirrors, with adiaphragm or aperture stop arranged at a location or position in adiaphragm plane in a first section of the optical path from a first usedarea to a second used area, with the position of the diaphragm beingdetermined by a location at which the chief ray of the central fieldpoint passes through the diaphragm plane, with the location of thediaphragm being at a radial distance from a second section of theoptical path extending from the second used area to a third used areathat is greater than 32% of the construction length of the lens, wherethe construction length of the lens is defined as the distance from theobject plane to the image plane along an optical axis of the projectionsystem. This embodiment also allows for an accessible diaphragm.

In the above mentioned embodiments the second used area is arrangedafter the first used area in the optical path from the object plane tothe image plane.

An alternative embodiment fulfils one of the above mentioned aspects bymeans of a microlithography projection lens or microlithographyprojection system especially for wavelengths ≦248 nm, preferably ≦193nm, in particular for EUV lithography for the preferred wavelengthsranging from 1-30 nm, for imaging an object field in an object planeonto an image field in an image plane, with the microlithographyprojection system comprising at least four mirrors, with the rays of abeam of light passing through the system from the object plane to theimage plane to impinge upon a used area of each of the said mirrors,wherein a diaphragm or aperture stop is provided at a position in adiaphragm plane in a second segment of the optical path from a secondused area to a third used area, with the location of the diaphragm beingat a first radial distance from a first section of the optical pathextending from a first used area to a second used area that is greaterthan 12% of the construction length of the projection system and asecond radial distance from a third section of the optical pathextending from the third used area to a fourth used area that is greaterthan 16% of the construction length of the projection system, where theconstruction length of the projection system is defined as the distancefrom the object field to be imaged to the image field along the opticalaxis of the projection system. This embodiment allows for an accessiblediaphragm from two sides of the diaphragm or aperture stop.

In the present application the useful or used area is defined as thearea on a mirror surface impinged upon by the rays of the beam of lightof the effective wavelength passing through the projection lens from theobject plane to the image plane. The effective wavelength is thewavelength A used to image an object in the object plane onto the imageplane. For instance, an effective wavelength in EUV lithography isλ=13.5 nm. Also other effective wavelengths can be used, e.g. λ=248 nmor λ=193 nm or λ=157 nm for UV-lithography. As a light source forEUV-lithography preferably a laser plasma sources is used. ForUV-lithography preferably lasers are used as light sources.

In the present invention in a preferred embodiment all optical elements,e.g. mirrors of the projection system are arranged physically, i.e.along the optical axis between the object plane and the image plane.

A radial distance to a beam of light traveling in the vicinity of thediaphragm in accordance with the embodiments described above allows in apreferred embodiment that the diaphragm is to be an iris stop, whenthere is sufficient space available for an iris stop construction in theabove embodiments. The advantage of iris diaphragms or iris aperturestops over interchangeable diaphragms is that the aperture can bealtered far easier as no diaphragm components need to be exchanged bymeans of a retooling device, with the leaves of the iris diaphragmsimply requiring actuation.

In one particularly preferred embodiment of the invention the positionor location of the diaphragm is selected such that apart from the beampassing through the diaphragm no beam of light runs within theprojection system above and/or below the diaphragm. This means that thediaphragm is freely accessible from both sides in a diaphragm plane. Inthe present application a radial direction is defined as a directionperpendicular to the direction of the principal axis HA of theprojection system. A direction in direction of the principal axis HA ofthe projection system is called a axial direction. A radial distance isa distance along the radial direction and a axial distance a distancealong the axial direction. Preferably, systems with an accessiblediaphragm from both sides in a diaphragm plane comprise a first group ofmirrors and a second group of mirrors, with the first group of mirrorsand the second group of mirrors arranged in such a physically separatedmanner that only a single beam of light from an object plane to an imageplane of the projection lens or projection system is formed from thefirst group of mirrors to the second group of mirrors. In the presentapplication physically separated means that there is an axial gap alongan optical axis HA of the projection lens or projection system betweenthe mirrors of the first group of mirrors and the mirrors of the secondgroup of mirrors. In the present application the gap between two mirrorsis defined as the axial separation of the vertices of two mirrorsurfaces along the optical axis.

In a further embodiment of the invention the axial distance between theiris diaphragm and the mirrors arranged physically in front of the irisdiaphragm and physically after the iris diaphragm is so large that theiris diaphragm can also be displaced axially, i.e. along the opticalaxis of the projection system. Displacing the diaphragm along theoptical axis allows the telecentric error resulting from diaphragmcurvature during opening and closing to be corrected.

Preferably, in order to permit such displacement, the physical distancealong the optical axis of the projection system from one mirror in thefirst group of mirrors SG1, with said mirror having the shortest axialdistance to the image plane, to one mirror in the second group ofmirrors SG2, with said mirror having the greatest axial distance to theimage plane, is greater than 0.1%, and preferably greater than 1%, mostpreferably greater than 5%, most preferably greater than 10% of theconstruction length of the system. This axial distance is the physicalaxial distance between the first and the second group of mirrors. Adiaphragm is arranged between the first and second group of mirrors.

In one particularly preferred embodiment of the invention, provision ismade for the physical axial distance between the first mirror with thefirst used area and the second mirror with the second used area, betweenwhich the diaphragm is arranged, to be greater than 40% of thestructural length or construction length of the projection system,preferably greater than 60% of the structural length of the projectionsystem, most preferably greater than 80% of the structural lenght of theprojection system. This has the further advantage that not only can thediaphragm be displaced along the axis, but the chief ray angle at thediaphragm is also small.

Preferably, the chief ray angle at the diaphragm is less than 24°,preferably less than 22°, and highly preferred is less than 20°, mostpreferably less than 18°, especially preferred less than 16° and inparticular less than 14°.

In order to provide a microlithography projection system that allows abroad tolerance with respect to diaphragm position and precision ofshaping of a diaphragm and a high image side numerical aperture amicrolithography projection system comprises at least two mirrors withan aperture stop arranged in the optical path between the two mirrorsand in a light path from one of the two mirrors to the other of the twomirrors. Furthermore no further optical element beside the aperture stopis situated the optical path from the one of the two mirrors to theother of the two mirrors and a chief ray passes through the aperturestop at an aperture angle <14° with respect to an optical axis (HA) ofthe projection system. Preferably the image-side numerical aperture (NA)of this system is greater or equal to 0.3, preferably greater or equalto 0.35, most preferably greater or equal to 0.4.

In a further embodiment of the invention in a microlithographyprojection system comprises at least two mirrors, wherein an aperturestop or diaphragm is arranged in the optical path between the twomirrors and in a light path from one of the two mirrors to the other ofthe two mirrors no further optical element is situated and the ratiobetween the aperture angle measured in degrees of the chief ray and theimage side numerical aperture NA is smaller or equal to 50, especiallysmaller or equal to 40, most preferably smaller or equal to 30.

If the aperture angle, e.g. at the diaphragm is 14° and the image sidenumerical aperture is NA=0.26 then the ratio of the aperture angle tothe image side numerical aperture NA is 14/0.3=46.6.

In a further embodiment of the invention the projection-lens isdeveloped in such a manner that the chief ray angle at which the beam oflight impinges on the mirror adjacent to the diaphragm is also less than24°, preferably less than 20°, and highly preferred less than 18°. Thechief ray angle at which the beam of light impinges on the mirror isdefined as the angle at which the chief ray, corresponding to thecentral field point, impinges upon the used or area with respect to thesurface normal.

The microlithography projection system in accordance with the inventioncan be provided with two, three, four, five, six, seven, eight or moreused areas and/or mirrors. The diaphragm or aperture stop can bearranged between each of the used areas. Arranging the diaphragm betweentwo used areas has the advantage that in comparison to embodiments withso-called front stops, the structural length or construction lengthand/or the chief ray angle at the illuminated object can be keptminimal.

If no mirror surface is employed twice, the number of used areascorresponds to the number of mirrors.

In a preferred embodiment of the invention a large numerical aperture(NA) at the image is achieved, preferably greater or equal to 0.3,preferably greater or equal to 0.35, most preferably greater or equal to0.4 with a very small chief ray angle at the diaphragm.

Preferably, the microlithography projection system provides for at leastone intermediate image.

In a further embodiment, the microlithography projection systemcomprises at least two intermediate images.

Intermediate images maintain the small diameter of the beam of lightpassing through the projection system from the object plane to the imageplane, thus also ensuring small mirrors, which are simpler tomanufacture as for instance there is no necessity for large andexpensive coating chambers.

In order to allow for the correction of the pupil-image, e.g. thecorrection of telecentricity and the distortion in a pupil plane of amicrolithography projection system for imaging an object field in anobject plane onto an image field in an image plane with a wavelength λis provided, wherein the microlithography projection system is acatoptric projection system comprising at least one intermediate imageof the object and an aperture stop in the optical path of a beam oflight from the object plane to the image plane. In such a projectionsystem diaphragm or aperture stop in the optical path is arranged orsituated behind the at least one intermediate image, i.e. the aperturestop is located optically between the at least one intermediate imageand the image plane. This allows for the arrangement of optical elementssuch as mirrors in the optical path of a light beam from the objectplane to the image plane before the aperture stop, i.e. opticallybetween the object plane and the aperture stop in order to set the chiefray angle at the object optimally. Furthermore there can be sufficientoptical elements provided in the light path behind the aperture stop,i.e. between the aperture stop and the image plane, to fulfill e.g. thetelecentricity specification on the image plane.

Preferably in such a microlithography projection system the aperturestop is arranged at a large axial distance from a used area. The axialdistance between the aperture stop and the used area is preferablygreater or equal to 0.1%, preferable greater or equal to 1%, mostpreferable greater or equal to 5%, most preferred greater or equal to10% of the construction length of the projection system.

In even a further embodiment of the invention with two intermediateimages, the microlithography projection system in accordance with theinvention is a 8-mirror microlithography projection system comprisingthree subsystems, with the first subsystem projecting the object fieldonto a first intermediate image of the object field, the secondsubsystem projecting the first intermediate image of the object fieldonto a second intermediate image of the object field and the thirdsubsystem projecting the second intermediate image of the object fieldonto the image field.

Preferably, provision is made in a system with a least an intermediateimage for the diaphragm to be in the beam of light propagating from theobject plane to the image plane after or behind the at least oneintermediate image. If the system comprises two intermediate images,then the aperture stop or diaphragm is situated after the firstintermediate image and in front of the second intermediate image.Consequently, in optical terms the aperture stop is arranged in thecenter of the projection system. This means that there are sufficientmeans of correction, i.e. mirrors with segments or used areas in thesection of the projection system or lens in front of the aperture stop,such that the chief ray angle at the object can be set optimally, andalso that there are sufficient means of correction in the section of theprojection system behind the aperture stop to fulfill the telecentricityspecification on the image plane.

The chief ray angle at the object is the angle at which the chief ray ofthe central field point impinges on the object on the object plane withrespect to the normal.

If the projection system comprises three subsystems, preferably, thethird subsystem comprises at least two used areas.

In one further developed embodiment the first subsystem comprises atleast two used areas.

In one particularly preferred embodiment the second subsystem comprisesat least two used areas.

In an preferred embodiment of the microlithography projection system asan 8-mirror projection system with preferably two intermediate images,the diaphragm is arranged between the fourth and fifth used area.

In a particularly preferred embodiment, the chief rays CR emanating fromeach point of the object enter the entrance pupil of themicrolithography projection system divergently with respect to theprincipal axis (HA) of the system. For systems involving the chief raysentering the entrance pupil divergently with respect to the opticalaxis, the entrance pupil of the lens lies in the optical path of aprojection exposure system with a projection system having a reflectiveobject situated in an object plane in front of the object plane of theprojection lens such as described in PCT/EP2003/000485.

The entrance pupil of a lens or projection system is defined in thisapplication as an image of the aperture stop imaged by the system partthat lies optically between the object and the aperture stop.

In one particularly preferred embodiment provision is made for a mirrorand/or a mirror surface to be employed twice. This means that a mirrorand/or a mirror surface is provided with two used areas. By using amirror surface in the optical path from the object to the image twice,it is possible to reduce the number of mirrors e.g. from eight to sevenor six mirrors.

Preferably the microlithography projection systems described before arecatoptric microlithography projection systems. Catoptricmicrolithography projection system have as optical elements onlyreflective optical elements such as mirrors for imaging an object in anobject plane into an image in an image plane.

In even a further embodiment the microlithography projection system is acatadioptric projection system. Catadioptric microlithography projectionsystems comprise reflective optical elements as well as refractiveoptical elements for imaging an object in an object plane into an imagein an image plane. For a man skilled in the art combinations of allpreferred embodiments amongst each other are possible without leavingthe scope of the invention.

In addition to the microlithography projection system, the inventionalso provides a projection exposure system. The projection exposuresystem comprises a light source to generate electromagnetic radiation,an illumination unit for partially collecting the radiation emitted fromthe light source and for transmitting it to illuminate an annular field,a structure-bearing mask on a substrate system, with this mask lying inthe plane of the annular field, and also a projection system inaccordance with the invention for projecting the illuminated part of thestructured mask onto an image field. A photosensitive substrate can bearranged on a substrate system.

Preferably the light source can be a EUV light source emitting EUVradiation with a wavelength ranging from 1-30 nm.

In addition to the microlithography projection system, the inventionalso provides a method for manufacturing microelectronic components, inparticular chips, using a projection exposure system comprising a lensof this kind. The method involves electromagnetic radiation, i.e. EUVradiation with wavelengths ranging from 1-30 nm emitted by a lightsource, illuminating via an illumination unit an annular field in aplane. A structured mask is arranged on a substrate system in the plane.Employing the projection system in accordance with the invention, theilluminated section of the mask is imaged onto an image field. Aphotosensitive substrate that constitutes part of a microelectroniccomponent can be arranged on a substrate system. A microelectroniccomponent, in particular a chip, can be produced as a result of multipleimaging steps involving the photosensitive substrate and developmentstages. This is known to those skilled in the art.

DESCRIPTION OF THE EMBODIMENTS

The invention will be described in greater detail below with the aid ofthe examples of embodiments and figures:

FIG. 1: shows the definition of the useful or used area of a mirror

FIG. 2: shows the shape of the field in the object and/or image plane ofthe lens

FIG. 3: shows a first embodiment of a projection system in accordancewith the invention

FIG. 4 a-c: show a second embodiment of a projection system inaccordance with the invention with eight used areas, where FIG. 4 bprovides the footprint of the beam of light in the diaphragm plane andFIG. 4 c the distortion along the field height in scanning direction inthe object plane.

FIG. 5 a-c: shows a third embodiment of a projection system inaccordance with the invention having eight used areas and eight mirrorsurfaces, and also a diaphragm that is freely accessible from two sidesin the y-z section, with FIG. 5 b providing the footprint of the beam oflight in the diaphragm plane. FIG. 5 c shows the distortion along thefield height in scanning direction in the object plane.

FIG. 6: shows a fourth embodiment of a projection system in accordancewith the invention, having eight used areas and eight mirror surfacesand also a diaphragm that is freely accessible from all sides

FIG. 7: shows the basic construction design of a projection exposuresystem with this type of microlithography projection system

FIG. 1 shows the useful or used area and the diameter of the useful orused area as defined in the present application.

FIG. 1 shows a kidney-shaped field as an example of an illuminated field1 on a mirror of the projection lens or projection system. A shape ofthis kind is expected for the used area when a lens in accordance withthe invention is employed in a microlithography projection exposuresystem. The enveloping circle 2 totally encompasses the kidney-shapedfield and coincides with the boundary 10 at two points 6, 8. Theenveloping circle is always the smallest circle which encompasses theused area. Consequently, the diameter D of the used area is a functionof the diameter of the enveloping circle 2.

FIG. 2 shows an example of the object field 11 of a EUV projectionexposure system in the object plane of the microlithography projectionsystem, imaged with the aid of the projection lens or projection systemin accordance with the invention on a image plane, in which aphotosensitive object, for instance a wafer, is arranged. The shape ofthe image field corresponds to that of the object field. Reductionlenses or reduction projection systems such as those used inmicrolithography reduce the image field by a specified factor, e.g. by afactor of 4, preferably a factor of 5, most preferably a factor of 6,even most preferably a factor of 7, especially preferably a factor of 8in comparison to the object field. For an EUV lithographic system, theobject field 11 has the shape of a segment of an annular field.

The segment has an axis of symmetry 12. Furthermore, FIG. 2 shows thecentral field point ZF of the annular field segment 11. In FIG. 2 SBdesignates the width of the field in scan orientation, also referred toas the scan slit width, s refers to the arc length and r the radius,i.e. the radial distance to the principal axis (HA).

In catoptric systems only reflective optical components such as mirrorsare used. In case of catoptric systems the preferred field in the imageplane is a annular field.

Catadioptric systems also contain transparent components in addition toreflective optical components. Catadioptric systems are also an aspectof the present invention. In case of catadioptric systems the preferredfield in the object plane is a rectangular field.

Furthermore, FIG. 2 indicates the axes spanning the object and/or imageplane, namely the x axis and the y axis. As shown in FIG. 2, the axis ofsymmetry 12 of the annular field 11 extends in the direction of the yaxis. At the same time the y axis coincides with the scan orientation ofan EUV projection exposure system, designed as an annular field scanner.The x axis is thus the orientation perpendicular to scan orientationwithin the object plane. FIG. 2 also shows the unit vector x in thedirection of the x axis.

The optical axis HA of the system extends along the z axis. Although aprojection system with eight used areas is described below as anexample, the invention is not restricted to such a system.Microlithography projection systems having three, four, five, six,seven, eight and more used areas being encompassed by the invention,where a diaphragm is arranged at a position in a first section of theoptical path from a first used area to a second used area, with thedistance from the diaphragm position to a second section of the opticalpath between a second used area and a third used area being greater than32% of the construction length of the projection system or projectionlens. The construction length is defined as the axial distance from theobject field to be imaged to the image field along the optical axis HA.

A further embodiment of the application describes projection lenses orprojection systems comprising at least four mirrors, with the rays of abeam of light passing through the lens from the object plane to theimage plane impinge upon a used area of each of the said mirrors, withprovision being made for a diaphragm at a position in a diaphragm planein a second section of the optical path from a second used area to athird used area, with the location of the diaphragm or aperture stopbeing at a first distance from a first section of the optical pathextending from a first used area to a second used area that is greaterthan 12% of the construction length of the lens or projection system,and the location of the diaphragm being at a second distance from athird section of the optical path extending from the third used area toa fourth used area that is greater than 16% of the construction lengthof the projection system, where the construction length of theprojection system is defined as the distance from the object field to beimaged to the image field along the optical axis.

FIG. 3 shows a first example of an embodiment of a catoptric projectionsystem that can be used e.g. in EUV-lithography with wavelengths λ<30 nmand that features a very small chief ray angle of just 14° at thediaphragm B at an aperture of NA=0.40.

The projection system projects or images an object in an object plane100 onto an image plane 102, on which for instance a wafer can bearranged.

FIG. 3 shows the local coordinate system in the object plane 100, inwhich a mask or so called reticle is arranged in a projection exposuresystem. The origin of the coordinate system lies on the optical axis HA.The principal axis (HA) of the projection lens extends along the z axis.The y axis designates the scan orientation as defined in FIG. 2. Theprojection lens in accordance with the invention comprises eight usedareas N1, N2, N3, N4, N5, N6, N7 and N8.

The first intermediate image Z1 lies in the optical path between asecond used area. N2 and a third used area N3. The diaphragm B lies inthe optical path between a fourth used area N4 and a fifth used area N5.The second intermediate image Z2 lies between the sixth used area N6 andthe seventh used area NT In the embodiment shown, the first subsystemSUB1 comprises the used areas N1 and N2, the second subsystem SUB2 theused areas N3, N4, N5 and N6, and the third subsystem SUBS the usedareas N7 and N8.

The example of the embodiment shown in FIG. 3 comprises eight mirrorsS1, S2, S3, S4, S5, S6, S7 and S8 having eight used areas N1, N2, N3,N4, N5, N6, N7 and N8. All eight mirrors S1, S2, S3, S4, S5, S6, S7 andS8 are aspherical mirrors. FIG. 3 also shows the y and z axes of the x,y, z coordinate system. The z axis extends parallel to the optical axisHA and the z axis projects from the object plane 100 to the image plane102. The y axis extends parallel to the axis of symmetry 12 of theobject field 11. The object field 11 is shown in FIG. 2. The y-z-planeshown in FIG. 3 is also denoted as meridional section.

The system is centered with respect to the optical axis HA and is on theimage side telecentric in the image plane 102. Image-side telecentricitymeans that the chief ray CR of the central field point ZF meets theimage plane 102 at an angle close to or approximating 0° with respect tothe normal, which is perpendicular to the object plane.

The projection system shown in FIG. 3 with eight used areas on eightmirrors and/or mirror surfaces is provided with an image-side apertureNA=0.4 and a scan slit width of 1 mm. To minimize the angle of incidenceon the single mirror surfaces, the chief ray angle at object 100 wasminimized, with the object-side aperture NAO=0.1. In this manner theangle of incidence is minimized on the first mirror. The maximum chiefray angle at the object is less than 6.5° in the case of the statedobject-side numerical aperture NAO of 0.1.

The exact specification of the projection system in accordance with FIG.3 in Code V format are given in the following Table 1:

TABLE 1 Optical data of Embodiment 1 according to FIG. 3 Surface RadiusThickness Mode Object INFINITY 751.558 Mirror 1 −1072.117 −601.471 REFLMirror 2 3903.145 1291.928 REFL Mirror 3 −1304.976 −1291.928 REFL Mirror4 19333.86 292.717 REFL STOP INFINITY 860.418 Mirror 5 −214134.818−560.864 REFL Mirror 6 993.495 699.657 REFL Mirror 7 171.261 −266.912REFL Mirror 6 325.575 324.897 REEL Image INFINITY 0 Surface K A B CMirror 1 0.00000E+00 −2.57399E−10 −6.47769E−17 −4.47874E−21 Mirror 20.00000E+00 −2.67579E−09 −8.22615E−14  2.10252E−19 Mirror 3 0.00000E+00 1.00633E−10 −2.02312E−16  3.13442E−22 Mirror 4 0.00000E+00 −5.06446E−09 1.65866E−14 −2.05299E−18 Mirror 5 0.00000E+00  2.53413E−10  8.10816E−16−5.92196E−21 Mirror 6 0.00000E+00  6.37357E−12  2.14262E−16 −7.84631E−22Mirror 7 0.00000E+00 −5.26794E−08  1.28356E−11  6.08242E−16 Mirror 80.00000E+00  2.04880E−10  2.23993E−15  2.00443E−20 Surface D E F GMirror 1 7.04837E−27  7.21766E−32  8.49831E−37  0.00000E+00 Mirror 22.23758E−21 −3.04749E−25  2.20843E−29  0.00000E+00 Mirror 3 1.47063E−28−2.10538E−33  3.20340E−39  0.00000E+00 Mirror 4 1.42606E−22 −2.61704E−27 5.14731E−32  0.00000E+00 Mirror 5 6.32909E−26 −3.91415E−31  3.23288E−37 0.00000E+00 Mirror 6 3.20130E−27 −4.60317E−33 −4.49165E−39  0.00000E+00Mirror 7 2.08602E−18 −8.11403E−22  1.18473E−25  0.00000E+00 Mirror 82.41505E−25 −2.74437E−31  5.36537E−35  0.00000E+00 Where: Object: Theposition of the object plane Mirror 1: Mirror S1 Mirror 2: Mirror S2Mirror 3: Mirror S3 Mirror 4: Mirror S4 Mirror 5: Mirror S5 Mirror 6:Mirror S6 Mirror 7: Mirror S7 Mirror 8: Mirror S8 STOP: aperture stop ordiaphragm Image: Position of the image plane K conical constant A, B, C,D, E, F, G aspherical coefficients

The upper, first part of Table 1 provides the general optical systemdata and the lower, second part the conical constant and the asphericalcoefficients of each single mirror surface.

Employing the projection system in accordance with the first example ofthe embodiment, shown in FIG. 3 and table 1, a chief ray angle isachieved at the diaphragm B on the diaphragm plane 1000 that is smallerthan 20°, namely just 14°. In the present case, the chief ray angle a atthe diaphragm is defined as the angle α at which the chief ray CR of thecentral field point ZF of the annular field in accordance with FIG. 2passes through the diaphragm plane 1000. In comparison withstate-of-the-art systems, for instance U.S. Pat. No. 6,781,671 B1, thepresent projection system has the advantage that the chief ray angle atthe diaphragm is minimal. With its minimal chief ray angle, thesingle-pass diaphragm has broader positional tolerances than previouslyshown state-of-the-art systems.

A further advantage of the system in accordance with the first exampleof the embodiment is that the sixth mirror S6 is arranged in axialdirection in front of the first mirror S1. This makes it is possible toarrange the fifth mirror S5 and sixth mirror S6 at great distances fromeach other physically, i.e. along the optical axis HA. The distancealong the optical axis from the vertex V6 of the sixth mirror S6 to thevertex V5 of the fifth mirror is greater than ⅓ of the constructionlength of the projection system. In this manner the beam of lightstrikes the used area of the mirror at a very low angle of incidence.

Arranging the third mirror S3 axially behind the sixth mirror S6 resultsin a large distance between the second mirror S2 and the third mirrorS3. This large distance and/or this large drift interval between S2 andS3 allows the angle of incidence of the beam of light that strikes theuseful area of the third mirror to be kept low.

Furthermore, in the example of the embodiment shown in FIG. 3 theoptical path from the first intermediate image Z1 to the third mirror S3is so great that large subapertures develop in the first intermediateimage Z1. In the present application a subaperture is defined as thefootprint of a single field point on a mirror, i.e. the zone illuminatedby a beam of light corresponding to a field point of a field, e.g. of anannular field, on a mirror surface impinged upon by the beam of light.Preferably, the diameter of the subaperture on the mirror is as large aspossible, in order to reduce the impact of contamination or defects onthe image as much as possible. The diameter of the subaperture isrelatively small on a mirror when the intermediate image is in thevicinity of the mirror.

FIGS. 4 a-4 c show a second embodiment of a projection system inaccordance with the invention having eight used areas N1, N2, N3, N4,N5, N6, N7 and N8. FIG. 4 shows a cross-section along the optical axisHA. Each used area corresponds to a mirror S1, S2, S3, S4, S5, S6, S7,S8, i.e. no mirror is utilized twice in the example of the embodimentshown. The same reference numbers apply to the same constructioncomponents as in FIG. 3. In particular, the x axis, the y axis and the zaxis are defined in the same manner as in the description of FIG. 3.

The projection lens is provided with an image-side NA of 0.35, with ascan slit width of 1 mm. The scan slit width SB in this applicationdesignates the extension of the field in accordance with FIG. 2 in scanorientation, i.e. along the y axis. A first intermediate image Z1 isprovided in the optical path between the second used area N2 and thethird used area N3 and a second intermediate image Z2 between the sixthused area N6 and seventh used area N7. The diaphragm B is arranged in adiaphragm plane 1000 between the fourth used area N4 and the fifth usedarea N5. The diaphragm plane 1000 is perpendicular to the principal axisHA of the projection system. The diaphragm plane is a x-y plane. As isapparent in FIG. 4 a, the diaphragm B is freely accessible, since nobeam of light extends in a radial direction R1 above the diaphragm B inthe projection system in the z-y plane. Consequently, the diaphragm B isfreely accessible from one side, in this case from above. The mean wavefront error of this system is less than 0.030 wavelengths. Consequently,image diffraction is restricted and image quality is suitable forlithographic purposes. The distortion of the system is less than 5 nm.

The Code V format data can be found in the following Table 2:

TABLE 2 Optical data of Embodiment 2 according to FIG. 4a-4c SurfaceRadius Thickness Mode Object INFINITY 620.863 Mirror 1 −1104.024−340.027 REFL Mirror 2 1841.922 1174.431 REFL Mirror 3 −1242.113−1305.267 REFL Mirror 4 2422.624 597.546 REFL STOP INFINITY 757.012Mirror 5 7641.802 −740.045 REFL Mirror 6 992.782 878.838 REFL Mirror 7167.22 −267.697 REFL Mirror 8 323.336 307.697 REFL Image INFINITY 0Surface K A B C Mirror 1  0.00000E+00 −9.05909E−10 −6.15434E−15−2.04482E−20 Mirror 2  0.00000E+00 −3.04349E−09  8.19174E−14−4.42149E−18 Mirror 3  0.00000E+00  3.64204E−10 −1.84948E−15 1.90679E−21 Mirror 4  0.00000E+00 −2.04780E−10 −2.72650E−14 3.19448E−19 Mirror 5  0.00000E+00 −8.67238E−10  5.08530E−14−1.78478E−18 Mirror 6  0.00000E+00 −7.28798E−10  4.66025E−15−1.31548E−20 Mirror 7  0.00000E+00  1.73357E−08  9.15221E−12−5.29307E−16 Mirror 8  0.00000E+00  2.05157E−10  2.33334E−15 2.60004E−20 Surface D E F G Mirror 1  2.86683E−24 −5.62387E−29 4.68166E−34 −8.89962E−40 Mirror 2  2.39762E−22 −8.45133E−27 1.66872E−31  0.00000E+00 Mirror 3  4.53503E−26 −3.13680E−31 8.92194E−37 −9.90478E−43 Mirror 4 −2.51097E−24  3.88684E−30 1.00805E−34  2.59035E−39 Mirror 5  4.08574E−23 −5.89266E−28 4.86735E−33 −1.77107E−38 Mirror 6 −1.81732E−26  1.97825E−31−3.41090E−37  0.00000E+00 Mirror 7  7.42366E−19 −2.77909E−22 5.22350E−26  0.00000E+00 Mirror 8  3.06861E−26  9.06962E−30−6.55480E−35  0.00000E+00 Where: Object : The position of the objectplane Mirror 1: Mirror S1 Mirror 2: Mirror S2 Mirror 3: Mirror 53 Mirror4: Mirror S4 Mirror 5: Mirror S5 Mirror 6: Mirror S6 Mirror 7: Mirror S7Mirror 8: Mirror S8 STOP: aperture stop or diaphragm Image: Position ofthe image plane K: conical constant A, B, C, D, E, F, G asphericalcoefficients

The upper, first part of Table 2 provides the general optical systemdata and the lower, second part the conical constant and asphericalcoefficients of each mirror surface.

FIG. 4 b shows the diaphragm plane 1000 of the projection lens inaccordance with FIG. 4. Clearly evident is the boundary 1030 of thediaphragm B, which lies in the diaphragm plane, and also the rays oflight 1020.1, 1020.2, 1020.3 extending below the diaphragm B in FIG. 4 afrom the used area N2 of the second mirror S2 to the third used area N3of the mirror S3. The sectional area formed by the intersection of therays 1020.1, 1020.2, 1020.3 of the beam of light traveling from thesecond to the third used area, with the diaphragm plane 1000, is alsoknown as the “footprint” of the beam of light. The footprint of the beamof light travelling from the used area N3 of the mirror S3 to the usedarea N4 of the mirror S4 is not shown in FIG. 4 b. As shown in FIG. 4 b,the radial distance RA1 of the rays of light 1020.2 from the position BOin the center of the diaphragm B is greater than 100 mm. The location BOof the diaphragm in the present embodiment coincides with the principalaxis HA. The radial distance RA2 of the rays of light 1020.1 from theboundary 1030 of the diaphragm B, developed here as a circle, is greaterthan 50 mm. The radial distance RA2 in the present application isdefined as a distance between the beam of light 1020.1 closest to theboundary 1030 of the aperture stop and the actual boundary 1030 of theaperture stop.

FIG. 4 c shows the distortion of the chief rays as a function of thefield height, i.e. the y-direction or scanning direction of the fieldshown in FIG. 2. In FIG. 4 c the distortion is shown in the objectplane. Since the system is a 4× reduction system 4 mm field height inthe object plane corresponds to 1 mm field height in the image plane. Asapparent from FIG. 4 c, the distortion is less than 6 nm.

FIGS. 5 a-5 c show a highly preferred embodiment of the invention. Inthe embodiment in accordance with FIGS. 5 a-5 c the diaphragm B isfreely accessible as no beam of light extends in a radial direction R1above nor below the diaphragm B in the projection system when imagingonto the z-y plane.

FIG. 5 a shows the cross-section along the optical axis HA. Freeaccessibility to the diaphragm is made possible by the specialconstruction of the projection system involving the division into twogroups of mirrors. The first group of mirrors SG1 comprises the usedareas N1, N2, N3, N4 on the mirrors S1, S2, S3 and S4. The second groupof mirrors SG2 comprises the used areas N5, N6, N7 and N8 on the mirrorsS5, S6, S7 and S8. The diaphragm B is arranged between the first groupof mirrors SG1 and the second group of mirrors SG2. Between first andthe second group of mirrors there is only one single optical path 150from the fourth used area N4 to the fifth used area N5, with saidoptical path passing through the diaphragm B only once. The diaphragm Bis arranged in a diaphragm plane 2000 between the mirror S1 in the firstgroup of mirrors SG1, with said mirror located at the shortest distanceA1 from the image plane 102, and the mirror S6 in the second group ofmirrors SG2, with said mirror located at the greatest geometric-physicaldistance A2 from the image plane 102.

The geometric-physical distance A1, A2 is defined in the presentapplication as for instance the distance of the vertex of each mirrorsurface upon which the used area is arranged to the image plane alongthe optical axis HA of the projection system. Mirror surfaces that arerotationally symmetrical around the optical axis HA are preferred.

As also shown in FIG. 5 a, in this embodiment of the invention thegroups of mirrors SG1, SG2 are spatially, i.e. physically geometrically,entirely separated from each other, i.e. a physical geometric distance Aexists between the group of mirrors as described below.

In order to allow sufficient space for displacement to correct thediaphragm error and telecentricity, in the present embodiment thedistance A=A1−A2, i.e. between the vertex V1 of the mirror S1 in thefirst group of mirrors SG1, with said mirror arranged closest to theimage plane 102, and the vertex V6 of the mirror S6 in the second groupof mirrors SG2, with said mirror arranged furthest from the image plane102, constitutes at least 0.1% of the construction length of theprojection system, preferably at least 1% of the construction length,more preferably at least 5% of the construction length, most preferablyat least 10% of the construction length.

In the case of the example of the embodiment shown in FIGS. 5 a-5 c, notonly is an intermediate image Z1 created in the first group of mirrorsSG1, but also an intermediate image Z2 in the second group of mirrorsSG2. Consequently, the diaphragm or aperture stop is arranged centrallyin the projection system permitting not only the correction of the pupilimage from the entrance pupil to the diaphragm plane, but also the pupilimage from the diaphragm plane to the exit pupil. This form ofcorrection is also possible in the other aspects of the embodiment shownin this application.

FIG. 5 b shows the diaphragm plane 2000 of the projection system inaccordance with FIG. 5 a. The boundary 2030 of the diaphragm B lying inthe diaphragm plane is easily recognizable. FIG. 5 b only shows theboundary 2030 of the annular aperture stop, as obviously no beams oflight pass through the diaphragm plane from the object-side to the imageside, apart from the beam of light passing through the diaphragm plane2000 as described above.

The 3rd example of the embodiment is provided with an object-sideaperture NA=0.30 and a scan slit length of 1 mm. The mean wave fronterror amounts to less than 0.015 wavelengths and the distortion amountsto less than 10 nm.

The following Table 3 provides the data of the system shown in FIG. 5a-5 c in Code V format:

TABLE 3 Optical data of Embodiment 3 according to FIG. 5a-5c SurfaceRadius Thickness Mode Object INFINITY 882.77 Mirror 1 −624.736 −504.089REFL Mirror 2 581.957 458.038 REFL Mirror 3 −812.068 −489.538 REFLMirror 4 11138.887 560.589 REFL STOP INFINITY 550.547 Mirror 5 −1447.424−148.098 REFL Mirror 6 635.352 286.891 REFL Mirror 7 144.805 −273.394REFL Mirror 8 319.043 313.394 REFL Image INFINITY 0 Surface K A B CMirror 1  0.00000E+00  7.73915E−10 −5.98212E−15  8.17237E−20 Mirror 2 0.00000E+00 −6.47101E−08 −9.54735E−12  3.78718E−15 Mirror 3 0.00000E+00 −1.54110E−10  3.09642E−16  2.61579E−20 Mirror 4 0.00000E+00  7.85369E−10 −8.14630E−15  2.18356E−19 Mirror 5 0.00000E+00  1.22682E−09  3.91275E−14 −1.29146E−18 Mirror 6 0.00000E+00  4.19491E−09 −4.70387E−14 −1.09647E−19 Mirror 7 0.00000E+00  2.62448E−08  4.35234E−11 −1.00119E−14 Mirror 8 0.00000E+00  1.40294E−10  1.66083E−15  2.07538E−20 Surface D E F GMirror 1 −8.36258E−25  5.39973E−30 −1.58497E−35  0.00000E+00 Mirror 2−5.40882E−19  3.92804E−23 −1.10963E−27  0.00000E+00 Mirror 3−3.42501E−25  2.39639E−30 −6.31181E−36  0.00000E+00 Mirror 4−4.02383E−24  4.72289E−29 −2.59578E−34  0.00000E+00 Mirror 5 0.00000E+00  4.41206E−28 −5.61328E−33  0.00000E+00 Mirror 6 0.00000E+00  8.75134E−29 −1.42696E−33  0.00000E+00 Mirror 7 8.74402E−18 −4.19879E−21  9.19439E−25  0.00000E+00 Mirror 8−1.58322E−25  1.74889E−29 −2.99873E−34  0.00000E+00 Where: Object: Theposition of the object plane Mirror 1: Mirror S1 Mirror 2: Mirror S2Mirror 3: Mirror S3 Mirror 4: Mirror S4 Mirror 5: Mirror S5 Mirror 6:Mirror S6 Mirror 7: Mirror S7 Mirror 8: Mirror S8 STOP: aperture stop ordiaphragm Image: Position of the image plane K: conical constant A, B,C, D, E, F, G aspherical coefficients

The upper, first part of Table 3 provides the general optical systemdata and the lower, second part the conical constant and the asphericalcoefficients of each mirror surface.

FIG. 5 c shows the distortion of the chief rays as a function of thefield height, i.e. the y-direction or scanning direction of the fieldshown in FIG. 2 in the object plane. As apparent from FIG. 5 c, thedistortion is less than 10 nm.

FIG. 6 shows a fourth example of the embodiment of the invention. Thesame reference numbers apply to the same construction components as inFIGS. 3 a to 5 c. The system in accordance with FIG. 6 is a systemhaving eight used areas N1, N2, N3, N4, N5, N6, N7 and N8, but onlyseven mirrors S1, S2, S3, S5, S6, and S7, as the surface of the firstmirror with the used areas N1 and N3 is employed twice. This allows theuse of one less mirror. As one mirror can be dispensed with in thisexample of the embodiment, production costs can be reduced.

The image-side numerical aperture NA of the system or lens in accordancewith FIG. 6 is 0.40 and the scan slit width is 3 mm, correlating withthe width of the annular field in scan orientation.

The optical specifications in accordance with FIG. 6 are given in thefollowing Table 4.

TABLE 4 Optical data of embodiment 4 according to FIG. 6 Surface RadiusThickness Mode Object INFINITY 578.724 Mirror 1 −581.864 −443.615 REFLMirror 2 5143.674 443.556 REFL Mirror 3 −581.864 −443.556 REFL Mirror 4−3202.338 301.549 REFL STOP INFINITY 839.439 Mirror 5 −3363.853 −714.456REFL Mirror 6 1281.674 853.249 REFL Mirror 7 157.692 −339.8 REFL Mirror8 390.985 379.8 REFL Image INFINITY 0 Surface K A B C Mirror 1 0.00000E+00  1.21362E−09 −2.31278E−14 3.01500E−19 Mirror 2  0.00000E+00−2.62732E−08  1.55172E−12 5.66333E−16 Mirror 3  0.00000E+00  1.21362E−09−2.31278E−14 3.01500E−19 Mirror 4  0.00000E+00  1.45633E−08 −9.26861E−133.72142E−17 Mirror 5  0.00000E+00 −5.33008E−11 −2.77433E−16 3.73061E−21Mirror 6  0.00000E+00 −1.08411E−10  1.49838E−16 2.06980E−22 Mirror 7 0.00000E+00  9.42477E−08  1.10318E−11 1.63255E−16 Mirror 8  0.00000E+00 9.45004E−11  7.08191E−16 2.55199E−21 Surface D E F G Mirror 1−1.60886E−24  0.00000E+00  0.00000E+00 0.00000E+00 Mirror 2 −4.73642E−20 0.00000E+00  0.00000E+00 0.00000E+00 Mirror 3 −1.60886E−24  0.00000E+00 0.00000E+00 0.00000E+00 Mirror 4 −6.39474 E−22  0.00000E+00 0.00000E+00 0.00000E+00 Mirror 5  0.00000E+00  0.00000E+00  0.00000E+000.00000E+00 Mirror 6  0.00000E+00  0.00000E+00  0.00000E+00 0.00000E+00Mirror 7  2.55464E−19  0.00000E+00  0.00000E+00 0.00000E+00 Mirror 8 8.24980E−26  0.00000E+00  0.00000E+00 0.00000E+00 Where: Object: Theposition of the object plane Mirror 1: Mirror S1 Mirror 2: Mirror S2Mirror 3: mirror S3 Mirror 4: Mirror S4 Mirror 5: Mirror S5 Mirror 6:Mirror S6 Mirror 7: Mirror S7 Mirror 8: Mirror S8 STOP: aperture stop ordiaphragm Image: Position of the image plane K: : conical constant A, B,C, D, E, F, G: aspherical coefficients

The upper, first part of Table 4 provides the general optical systemdata and the lower, second part the conical constant and the asphericalcoefficients of each single mirror surfaces.

FIG. 7 shows a projection exposure system for microlithography with aprojection lens in accordance with the invention having eight used areas200. The illumination system 202 is a illumination system as describedfor instance in EP 99106348.8 with the title “Beleuchtungssystem,insbesondere für die EUV-Lithographie” or in U.S. Pat. No. 6,198,793 B1with the title “Illumination system particularly for EUV-Lithography”,with the content of their disclosure having been fully incorporated intothe present application. An illumination system of this kind comprisesan EUV light source 204. The light from the EUV light source iscollected by the collector mirror 206. The reticle 212 is illuminated bymeans of a first mirror 207 comprising raster elements—so-called fieldhoneycombs—and a second mirror 208 comprising raster elements—so-calledpupil honeycombs—and also a mirror 210. The light reflected from thereticle 212 is imaged by means of the projection lens in accordance withthe invention on a substrate 214 comprising a photosensitive coating.

The invention discloses a projection lens or projection system for thefirst time that features the application of an iris diaphragm as theaperture stop especially in a catoptric projection system for e.g. EUVwavelengths within λ=11 to 30 nm, constituting a particularlyadvantageous and compact projection lens or projection system fromtechnical design and manufacturing points of view.

Moreover, the projection system presented features a large aperture witha simultaneous vignette-free and/or obscuration-free optical path. Thisculminates in a vignette-free exit pupil.

In particular, the invention discloses for the first timemicrolithography projection lenses for wavelengths ≦248 nm, preferably≦193 nm, in particular for EUV lithography for wavelengths ranging from1-30 nm for imaging an object field in an object plane onto an imagefield in an image plane, which are developed in such a manner thatprovision is made for an accessible diaphragm plane, into which forinstance an iris diaphragm can be introduced.

The invention claimed is:
 1. A projection system configured to imageradiation along an optical path from an object field in an object planeof the projection system into an image field in an image plane of theprojection system, the projection system comprising: an aperture stop,wherein: the projection system has two intermediate images of an objectin the object field of the projection system; the aperture stop is inthe optical path between the first and second intermediate images of anobject; and the projection system is a catoptric microlithographyprojection system.
 2. The projection system of claim 1, wherein theaperture stop comprises an iris diaphragm.
 3. The projection system ofclaim 2, comprising a mirror having a used area, wherein the aperturestop is disposed a distance from the used area of the mirror, and thedistance is at least 0.1% of a construction length of the projectionsystem.
 4. The projection system of claim 3, comprising at least fourmirrors, wherein each of the at least four mirrors has a used area. 5.The projection system of claim 3, comprising eight mirrors, wherein eachmirror has a used area.
 6. The projection system of claim 5, wherein theradiation has a wavelength that is at most 248 nm.
 7. The projectionsystem of claim 6, comprising: a first group of mirrors comprising afirst mirror; and a second group of mirrors comprising a second mirror,wherein: the aperture stop is in a diaphragm plane between the first andsecond groups of mirrors; the optical path intersects the diaphragmplane only once; the first group of mirrors is physically geometricallyseparated from the second group of mirrors along an optical axis of theprojection system.
 8. The projection system of claim 7, wherein: theaperture stop is between the first and second mirrors; the first mirroris a first axial distance from the image plane of the projection system;the second mirror is a second axial distance from the image plane of theprojection system; and the first axial distance is greater than thesecond axial distance.
 9. The projection system of claim 8, wherein thesecond axial distance is at least 0.3 times the first axial distance.10. The projection system of claim 1, wherein the aperture stop isdisposed a distance from a used area, and the distance is at least 0.1%of a construction length the projection system.
 11. The projectionsystem of claim 1, comprising at least four mirrors, wherein each of theat least four mirrors has a used area.
 12. The projection system ofclaim 1, comprising eight mirrors, wherein each mirror has a used area.13. The projection system of claim 1, wherein the radiation has awavelength that is at most 248 nm.
 14. The projection system of claim 1,comprising: a first group of mirrors comprising a first mirror; and asecond group of mirrors comprising a second mirror, wherein: theaperture stop is in a diaphragm plane between the first and secondgroups of mirrors; the optical path intersects the diaphragm plane onlyonce; the first group of mirrors is physically geometrically separatedfrom the second group of mirrors along an optical axis of the projectionsystem.
 15. The projection system of claim 14, wherein: the aperturestop is between the first and second mirrors; the first mirror is afirst axial distance from the image plane of the projection system; thesecond mirror is a second axial distance from the image plane of theprojection system; and the first axial distance is greater than thesecond axial distance.
 16. The projection system of claim 15, whereinthe second axial distance is at least 0.3 times the first axialdistance.
 17. A projection exposure system, comprising: amicrolithography illumination system; and a catoptric microlithographyprojection system configured to image radiation along an optical pathfrom an object field in an object plane of the catoptricmicrolithography projection system into an image field in an image planeof the catoptric microlithography projection system, the catoptricmicrolithography projection system comprising an aperture stop, wherein:the catoptric microlithography projection system has two intermediateimages of an object in the object field of the catoptricmicrolithography projection system; the aperture stop is in the opticalpath between the first and second intermediate images of the object; andthe projection exposure system is a microlithography projection exposuresystem.
 18. The projection exposure system of claim 17, wherein theaperture stop comprises an iris diaphragm.
 19. The projection exposuresystem of claim 17, comprising at least four mirrors, wherein each ofthe at least four mirrors has a used area.
 20. A method, comprisingusing the projection exposure system of claim 17 to produce amicroelectronic product.